Device for self-correction of position for semi-submersible platform



Dec. 22; 1 70 G. MONNEREAU DEVICE FOR SELF-CORRECTION 0F POSITION FORSEMI-SUBMERSIBLE PLATFORM Filed April 14, 1969 2 Sheets-Sheet 1 FIG-1FIG. 2

Dec. 22, 1970 x 5, MONNEREAU @fiflfififi DEVICE FOR SELF-CORRECTION 0FPOSITION FOR SEMI-SUBMERSIBLE PLATFORM 7 Filed April 14, 1969 2Sheets-Sheet a United States Patent Ofi'ice 3,548,602 DEVICE FORSELF-CORRECTION OF POSITION FOR SEMI-SUBMERSIBLE PLATFORM GeorgesMonnereau, Paris, France, assignor to Compagnie Generale dAutomatisme,Paris, France Filed Apr. 14, 1969, Ser. No. 815,582 Claims priority,application France, Apr. 12, 1968,

Int. Cl. E02b 17 B631) 35/44 US. Cl. 61-46 8 Claims ABSTRACT OF THEDISCLOSURE A disc-shaped element which can be inclined at will resiststhe disturbances due to the swell acting on submersible platformsfloating or anchored to the bottom of the sea.

BACKGROUND OF THE INVENTION (1) Field of the invention It is known thatsuch structures are used both as observation bases and as platforms foroil drilling at sea. It is also known that such platforms have to bestable to swell in order to be usable. For floating platforms in theopen sea it is known from French Pat. No. 1,510,937 of 30, Nov. 1966 bythe applicant Company for Improvement in Floating Platforms that adiscoidal element arranged about each vertical structure and submergedto the desired depth annuls the action of the swell.

Likewise, for platforms arranged in the vicinity of the coast it issufiicient to fix the lower end of a cylindrical structure on the bottomby a ball joint fastening in order to obtain stability of the platformmounted on the unitary cylindrical structure.

However, the swell is not the only disturbing element for suchplatforms, which are also subjected both to the action of the wind andto the action of sea currents.

For floating platforms, this results in a general drifting of theplatform, the position of which is no longer fixed. For platformsanchored along the coast a torque is exerted on the cylindricalstructure which is then rotated about its ball joint fastening andbegins to oscillate on either side of a mean position inclined relativeto the vertical.

SUMMARY OF THE INVENTION The object of the present invention is toeliminate respectively the drifting of floating platforms and theinclination relative to the vertical of cylindrical structures which areanchored on the sea bed by using a discoidal element having its axis ofsymmetry coinciding with the axis of the vertical structure andoptionally inclinable.

Tests in a swell tank on a small-scale model have shown that the swellexerted on the inclined discoidal element creates a force opposing thedrift due to the current. It is then sufficient, to annual the drift, todetermine the value of the parameters relative to the discoidal element;its dimension, its angle of inclination and its immersion depth.

In a similar manner, after tests, a cylindrical model anchored with aball joint to the bottom of the tank, inclined under the action of thecurrent and oscillating 3,548,602 Patented Dec. 22, 1970 about this meanposition, was returned to the vertical and oscillated with a reducedamplitude by arranging a discoidal element about it, submerged in thevicinity of the water surface level, and suitably inclined.

A device for self-correction of position according to the invention fora semi-submersible platform mounted on at least one partially submeredsupport of hollow cylindrical form with a vertical axis and having alength substantially greater than the diameter, is characterized in thata discoidal element centered on the axis of the cylindrical support isoptionally inclinable in accordance with the direction of the swell andsubmerged in the vicinity of the sea surface level.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows in horizontal projection,an inclined disc mounted on a vertical cylindrical structure.

FIGS. 2 and 3 are partial views, in elevation, in two directionsperpendicular to one another, a vertical structure with optionallyinclinable disc.

FIG. 4 is a diagrammatic view, in elevation, of a platform supported bya single vertical structure with symbolic representation of an inclineddisc.

lFIG. 5 shows in symbolic manner, structures anchored to the bed andinclined by a current and their reutrn to the vertical by means of asuitably inclined disc.

DESCRIPTION OF PREFERRED EMBODIMENTS The plane inclined disc 1 in FIGS.1, 2 and 3 is mounted by universal joint means including a ring 2 on thehollow cylindrical structure 3 which has a vertical axis 9. The disc 1is perforated with a central aperture 4 permitting its free orientationpermit-ted by the universal joint type of mounting. The disc 1 isadapted to rotate relative to the ring 2 on the axis 5 common to the twostuds 6 fixed to the said ring and on which it is mounted. On the otherhand the ring 2 can rotate about two other studs 7 fixed to thecylindrical structure 3 and define an axis 8 perpendicular to the axis5, the two axes intersecting on the axis of symmetry 9 of the verticalstructure.

In FIG. 4 the floating platform symbolized by a working stage 10 ismounted on a single vertical cylindrical structure 11 stabilized by ahollow anti-swell disc 12 connected to the cylinder 11 by the chamber 13serving as a machine room. Columns 14 participate in supporting theplatform and columns 15 fixed below the disc 12 serve to support thecounter-weight 16 intended to lower the center of gravity of theplatform.

The inclined disc according to the invention is shown at 17, and mountedwith a universal joint type of connection on the cylinder 11 by means ofthe ring 18 and is submerged in the vicinity of the average surfacelevel 19 of the sea and subjected to the effects of the swell which hasa sinusoidal profile 20 at the surface.

The inclined disc is sensitive to the swell and accepts a proportion ofthe energy thereof to effect either the displacement of the latter ifthere is no current or the annulling of its displacement in the case ofdrift.

When the swell is in the direction of the arrow 21 the platform isdriven in the direction of the double-line arrow 22 owing to the actionof the swell on the disc 17.

Similarly, in the case of a swell in the direction of the broken-linearrow 23, the disc 17, still in the same inclination, undergoes thereaction of the swell and the floating platform is urged in thedirection indicated by the brokenline double arrow 24. Therefore,whatever the direction of the swell, the direction in which the platformis entrained depends on the inclination of the disc 17.

The inclined disc 17 is shown in circular form, with ellipticalprojection on any plane forming an angle with its own plane; but it hasbeen found on models, that the effect of the swell can be accentuated byincreasing the dimensions thereof in accordance with the inclination,that is to say the greater inclination. For example it is possible touse an elliptical-section disc, the minor axis of the ellipse remaininghorizontal and the major axis being arranged in accordance with thegreater inclination. Instead of the ellipse, a rectangular profile maybe chosen for the disc 17, the longest side of the rectangle beingarranged in accordance with the inclination. In any case the center ofthe profile selected, about which the universal joint connection allowsthe disc 17 to pivot, should be situated on the axis of symmetry 25 ofthe cylindrical structure 11 of the floating platform in order toprevent any asymmetrical reaction of the swell.

In FIG. 5, the cylindrical structure 26 anchored to the bed of the sea27 by a ball joint fastening 28 remains in a vertical position as longas no disturbing phenomenon intervenes.

The same structure moved out of its vertical position by disturbances isshown in oblique positions respectively at 29 and 30.

Owing to the discoidal element according to the invention, it ispossible to return the oblique structure to the vertical by the actionof the swell on the suitably arranged element. When the swell isdirected in accordance with arrow 31, the discoidal element is inclinedas shown by the symbolic line 32 and permits returning of the structurefrom the oblique position 29 to the vertical position 26.

Similarly the structure in the oblique position 30 is returned to thevertical position 26 when, with the swell in the direction of thebroken-line arrow 33, the discoidal element is placed in an inclinedposition 34 as shown in broken lines. Indeed, if it is arranged that theperpendicular to the plane of the discoidal element is directed towardsthe surface of the sea, the average level of which is 19, thecylindrical surface supporting it tends to be displaced in the directionof the horizontal projection of the directed perpendicular. In additionthe oscillations of the structure returned to the vertical are reducedrelative to oscillations in the oblique position.

What is claimed is:

1. A device for self-correction of position for semisubmersible platformmounted on at least one partly submerged support of hollow cylindricalform with a vertical axis and having a length substantially greater thanthe 4 diameter, said devcie comprising a discoidal element centered onthe axis of the said cylindrical support and optionally inclinable inaccordance with the direction of the swell and submerged in the vicinityof the surface level of the sea.

2. The self-correction device according to claim 1, wherein theinclinable discoidal element pivots about its center by means of auniversal joint connection.

3. The self-correction device according to claim 2, wherein saiduniversal joint connection includes an intermediate ring centered on theaxis of the vertical cylindrical structure.

4. The self-correction device according to claim 1, wherein theinclinable discoidal element is circular and centrally apertured.

5. The self-correction device according to claim 1, wherein theinclinable discoidal element is centered on the axis of the cylindricalvertical structure and is of increased size in the direction of itsgreater inclination.

6. The self-correction device according to claim 1, wherein theinclinable discoidal element is elliptical and the major axis of theellipse corresponds with its greater inclination.

7. The self-correction device according to claim 1, wherein theinclinable discoidal element is rectangular and the longest side of therectangle is situated in the direction of the greater inclination of thesaid element.

8. The self-correction device according to claim 1, wherein saidsemi-submersible platform is anchored to the sea bed by the verticalstructure to ensure that the said structure is kept vertical.

References Cited UNITED STATES PATENTS 2,897,654 8/1959 Harris 6l-46X3,390,654 7/1968 Bromell et al 1l4.5

3,407,767 10/1968 McClintock et a1 114.5

FOREIGN PATENTS 1,510,937 12/1967 France 6 1-465 J. KARL BELL, PrimaryExaminer US. Cl. X.R.

